Sera of patients with various liver diseases exhibit binding activity for polymerized human serum albumin (pHSA). It is controversial whether this albumin binding activity is related to receptors on HBsAg or antibodies to pHSA. Passive hemagglutination of pHSA-coated red blood cells has been employed to detect and quantitate albumin binding activity in human sera. An indirect fluorescent antibody method has been developed in our laboratory to determine whether HBsAg or immunoglobulins or both react with pHSA-coated red blood cells. Hemagglutination inhibition using polymeric, monomeric and native HSA and heterologous albumin has been used by us to determine the specificity of the albumin binding factors. These methods will be employed to characterize albumin binding activity in sera in order to determine their significance in liver disease. In addition, we will compare the conditions that influence antibody and receptor mediated pHSA binding. In the second phase of the proposed project, we will study pHSA receptors and their relation to HBsAg and albumin at the cellular and subcellular levels. Three hepatocellular carcinoma cell lines that produce HBsAg with pHSA receptors (PLC/PRF/5), albumin (Hep G2) or both (Hep 3B) will be investigated by immunohistochemical methods at the light and electron microscopic levels for the presence of pHSA receptors, HBsAg and albumin in the cytoplasm and on the cell surface. Similar studies will be applied to liver biopsy specimens from patients with various liver diseases and may yield information concerning the biology of hepatitis B virus and its effect on hepatocytes.